1. Field of the Invention
The present invention relates to a display device which performs a display control of pixels using thin film transistors (TFTs) and a manufacturing method thereof.
2. Description of the Related Art
For example, among various display devices including a liquid crystal display device, there has been known a display device which performs a display control of respective pixels by an active matrix drive method using thin film transistors. In such a display device, a plurality of scanning signal lines and a plurality of video signal lines are arranged on a substrate (hereinafter, referred to as a TFT substrate) in a stereoscopically intersecting manner. Here, respective intersecting points of the scanning signal lines and the video signal lines correspond to the pixels of the display device. A portion of the scanning signal line functions as a gate electrode of the thin film transistor, and either one of a drain electrode and a source electrode (the drain electrode in the explanation made hereinafter) of the thin film transistor is connected to the video signal line. Further, a pixel electrode is connected to the electrode of the thin film transistor which is not connected to the video signal line (source electrode in the explanation made hereinafter). Due to such constitution, by applying voltages to both of the scanning signal line and the video signal line corresponding to the pixel to which a display control is applied, the voltages are applied to the corresponding pixel electrode via the thin film transistor which functions as a switching element so that a display control of the pixel can be performed.
To form such a thin film transistor, it is necessary to stack the scanning signal lines, an insulation film, a semiconductor layer, and a conductor layer on the TFT substrate in this order. Here, the conductor layer is a layer which includes the video signal lines, the drain electrodes and the source electrodes. To form these scanning signal lines, a semiconductor layer and a conductor layer having desired patterns respectively on the TFT substrate, a so-called photolithography technique can be used. According to this technique, a resist material is applied to a surface of a material film for forming these parts by coating, the resist material is processed in a pattern of these parts to be formed by exposure and development, and the material film for forming these parts is etched using the processed resist material as a mask thus forming the scanning signal lines, the semiconductor layer and the conductor layer having desired patterns.
Further, in forming the semiconductor layers and the conductor layers by performing exposure one time, a resist reflow method may be adopted (see JP-A-2002-90779 (corresponding U.S. Pat. No. 6,933,989B2) (patent document 1), for example). In this method, a material film for forming a semiconductor and a material film for forming a conductor are sequentially stacked on a TFT substrate on which scanning signal lines and an insulation film are formed, the material film for forming the conductor is formed into conductor layers of a desired pattern by the above-mentioned technique and, thereafter, a resist material remaining on the conductor layers is melted. Due to such steps, the resist material covers a region which is larger than a region on which the conductor layer is formed. By further etching the material film for forming the semiconductor using the spread resist material as a mask, the semiconductor layers are formed into a shape which includes a region where the conductor layer is formed without exposing the resist material.
Further, in a display device having the above-mentioned type of thin film transistor, an opening portion may be formed in a portion of a scanning signal line where the scanning signal line intersects the video signal line (see JP-A-9-258244 (patent document 2), for example). By forming the opening portion in the scanning signal line, the scanning signal line is bifurcated at the portion where the opening portion is formed so that, as viewed in a plan view, the respective branched or bifurcated scanning signal lines intersect with the video signal line. Due to such constitution, when the scanning signal line and the video signal line are short-circuited with each other at a portion of an intersecting portion during a manufacturing process by a chance, by cutting one scanning signal line out of these bifurcated or branched scanning signal lines, it is possible to cut off only the portion which is short-circuited with the video signal line from the whole scanning signal line.
Further, as described in patent document 2, a connecting line which connects the video signal line and the drain electrode of the thin film transistor may be formed such that the connecting line is branched from the video signal line above the opening portion. Due to such constitution, when it is necessary to correct a certain pixel, it is possible to separate the video signal line and the thin film transistor from each other by cutting the connecting line which connects the drain electrode of the thin film transistor corresponding to the pixel and the video signal line above the opening portion. Accordingly, in case of pixels which are operated in a normally black mode, it is possible to fix liquid crystal at a state which interrupts light (black spot forming).